Filesystem Hierarchy Standard

The /var/tmp directory is made available for programs that require
temporary files or directories that are preserved between system reboots.
Therefore, data stored in /var/tmp is more persistent than data
in /tmp.

Files and directories located in /var/tmp must not be deleted
when the system is booted. Although data stored in /var/tmp
is typically deleted in a site-specific manner, it is recommended that
deletions occur at a less frequent interval than /tmp.